1. Technical Field
The invention relates to a method and a device for producing a piston for an internal combustion engine and to a piston for an internal combustion engine.
When intended for diesel engines, almost one hundred percent of pistons for internal combustion engines are produced by means of gravity die casting. This also applies to a large proportion of pistons for Otto engines. Within the framework of the development of smaller and smaller, but at the same time more efficient engines, greater and greater compressive stresses occur. This means greater stressing of the first piston ring and the first ring groove of the piston in which the latter is accommodated. In particular, in the future highly stressed pistons for Otto engines will have to be provided with anti-wear reinforcement in order to improve the life span and the operating characteristics of the pistons and piston rings.
2. Related Art
In the field of Otto engine pistons previously used items are known wherein the highly stressed first ring groove is reinforced locally with an electrically applied aluminium oxide layer in order to withstand the high surface pressures and wear stresses in the first ring groove.
With diesel engine pistons it is already standard, and it could increasingly become a requirement for Otto engine pistons, to cast ring carriers integrally; from a technical point of view, however, this is very complex. In the domain in question it is known, furthermore, in particular for diesel engine pistons which normally have a cooling duct, to insert a ring carrier which is combined with a cooling duct manually into the die. Said ring carrier can be immersed into liquid aluminium before placing into the die using the so-called Alfin method, and so is totally wetted with partially solidified aluminium upon recasting. This means particularly good metallic bonding between the ring carrier and the surrounding piston material. The cooling duct can have a mould core, for example made of salt, which can be washed out after solidification of the piston blank.
A method is known from DE 198 07 176 C2 for producing a piston for an internal combustion engine according to the preamble to Claim 1 wherein the section of the uppermost ring groove and the cooling duct is at first recessed, and is then covered by a radially inwardly stretched covering ring so that the remaining groove, from which the ring groove is later cut, can subsequently be filled, for example by thermal injection.
According to DE 196 49 363 C2 the section in question is formed by a melting core the outer ring of which is later removed in order to fill this section with reinforcement material. Subsequently, the inner section of the melting core is also removed in order to form the cooling duct.
EP 1536 125 A1 describes a piston in which there is a recess in the upper part of the piston which is closed by a covering element in one or more parts in order to form a cooling duct.
A method emerges from DE 10 2004 003 980 A1 for producing a closed cooling duct of a piston made of forged steel wherein initially a radially outwardly facing circumferential opening is turned in and which is subsequently closed by two semi-circular elements.
WO 82/03814 A1 relates to a method for producing a piston, wherein the section of a piston ring groove is initially cut, and is subsequently processed with an electron or laser beam in order to form an alloy section. The piston ring groove is then cut out of the section treated in this way.
Finally, DE 10 2005 047 035 B3 describes a method for producing a piston for an internal combustion engine wherein only the cooling duct is filled with a removeable mass, and the outer radial groove, from which the first ring groove is later cut, is filled with reinforcement material. Next the removeable mass is removed so that a ring-shaped cooling duct remains.